U.S. patent number 8,377,193 [Application Number 12/920,216] was granted by the patent office on 2013-02-19 for dispersion comprising hydrophobized silicon dioxide particles.
This patent grant is currently assigned to Evonik Degussa GmbH. The grantee listed for this patent is Uwe Diener, Wolfgang Lortz, Gabriele Perlet, Sascha Reitz. Invention is credited to Uwe Diener, Wolfgang Lortz, Gabriele Perlet, Sascha Reitz.
United States Patent |
8,377,193 |
Lortz , et al. |
February 19, 2013 |
Dispersion comprising hydrophobized silicon dioxide particles
Abstract
Aqueous dispersion which comprises hydrophobized silicon dioxide
particles and in each case one or more dispersing additives, a
basic composition, and which is free of color pigments, inactive
fillers and binders, in which the hydrophobized silicon dioxide
particles have a methanol wettability of 30 to 60 and are present
in the dispersion with a proportion of 0.1 to 50% by weight,--the
proportion of water is 30 to 90% by weight based on the
dispersion,--the dispersing additive is at least one phosphate
ester of an ethoxylated alcohol having 8 to 18 carbon atoms, the
proportion of which is 3 to 25% by weight based on the proportion
of the hydrophobized silicon dioxide particles,--the basic
composition comprises or consists of one or more amines of the
general formula RNH.sub.2, R.sub.2NH and R.sub.3N, where R is an
alkyl group or a hydroxyl-substituted alkyl group having in each
case 2 to 10 carbon atoms, and is present with a proportion of 5 to
30% by weight based on the proportion of hydrophobized silicon
dioxide particles,--the dispersion further comprises one or more
polyols having 2 to 15 carbon atoms, the proportion of which is 1
to 10% by weight based on the proportion of hydrophobized silicon
dioxide particles,--the pH of the dispersion being 9 to 11.
Inventors: |
Lortz; Wolfgang (Waechtersbach,
DE), Perlet; Gabriele (Grosskrotzenburg,
DE), Diener; Uwe (Grosskrotzenburg, DE),
Reitz; Sascha (Hanau, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lortz; Wolfgang
Perlet; Gabriele
Diener; Uwe
Reitz; Sascha |
Waechtersbach
Grosskrotzenburg
Grosskrotzenburg
Hanau |
N/A
N/A
N/A
N/A |
DE
DE
DE
DE |
|
|
Assignee: |
Evonik Degussa GmbH (Essen,
DE)
|
Family
ID: |
39720456 |
Appl.
No.: |
12/920,216 |
Filed: |
March 5, 2009 |
PCT
Filed: |
March 05, 2009 |
PCT No.: |
PCT/EP2009/052581 |
371(c)(1),(2),(4) Date: |
August 30, 2010 |
PCT
Pub. No.: |
WO2009/121680 |
PCT
Pub. Date: |
October 08, 2009 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20110000397 A1 |
Jan 6, 2011 |
|
Foreign Application Priority Data
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|
|
|
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Apr 2, 2008 [EP] |
|
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08103321 |
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Current U.S.
Class: |
106/481; 516/34;
106/287.29 |
Current CPC
Class: |
C09D
7/45 (20180101); C09D 7/43 (20180101); C09D
7/62 (20180101); B82Y 30/00 (20130101); C09C
1/3063 (20130101); C09D 5/027 (20130101); C09C
1/3072 (20130101); B01F 17/0007 (20130101); B01F
17/0064 (20130101); C01P 2006/90 (20130101); C01P
2004/64 (20130101); C01P 2004/62 (20130101); C01P
2006/22 (20130101); C01P 2004/61 (20130101); C01P
2006/12 (20130101); C08K 3/36 (20130101) |
Current International
Class: |
C04B
14/04 (20060101); C09K 17/02 (20060101); B01F
3/12 (20060101) |
Field of
Search: |
;106/481,297
;516/34 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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103 16 661 |
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Nov 2004 |
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DE |
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10 2006 020 987 |
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Nov 2007 |
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DE |
|
Primary Examiner: Ali; Shuangyi Abu
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, L.L.P.
Claims
The invention claimed is:
1. An aqueous dispersion which comprises hydrophobized silicon
dioxide particles, at least one polyol having 2 to 15 carbon atoms,
at least one dispersing additive, a basic composition, and no color
pigments, no inactive fillers, and no binders, wherein: the
hydrophobized silicon dioxide particles have a methanol wettability
of 30 to 60 and are present in the dispersion with a proportion of
0.1 to 50% by weight based on the dispersion; a proportion of water
is 30 to 90% by weight based on the dispersion; the dispersing
additive is at least one phosphate ester of an ethoxylated alcohol
having 8 to 18 carbon atoms, a proportion of which is 3 to 25% by
weight based on the proportion of the hydrophobized silicon dioxide
particles; the basic composition comprises at least one amine of
formulas RNH.sub.2, R.sub.2NH, and/or R.sub.3N wherein R is an
alkyl group or a hydroxyl-substituted alkyl group having in each
case 2 to 10 carbon atoms, and is present with a proportion of 5 to
30% by weight based on the proportion of hydrophobized silicon
dioxide particles; the at least one polyol is present with a
proportion of 1 to 10% by weight based on the proportion of
hydrophobized silicon dioxide particles; the phosphate ester, the
basic composition, and the at least one polyol are soluble in an
aqueous phase of the dispersion; and the pH of the dispersion is 9
to 11.
2. The aqueous dispersion according to claim 1, wherein the
methanol wettability is 35 to 55.
3. The aqueous dispersion according to claim 1, wherein the
hydrophobized silicon dioxide particles are obtained by a fuming
process.
4. The aqueous dispersion according to claim 1, the wherein a mean
particle size (median) of the hydrophobized silicon dioxide
particles is 200 nm or less.
5. The aqueous dispersion according to claim 1, wherein the
phosphate ester is a mono-, di-, and/or trisubstituted phosphate
ester of an ethoxylated primary alcohol with one, two, or three
linear C.sub.12-C.sub.14 carbon chains.
6. The aqueous dispersion according to claim 1, comprising
N,N-dimethylethanolamine.
7. The aqueous dispersion according to claim 1, comprising at least
one selected from the group consisting of tripropylene glycol and
2,4,7,9-tetramethyldec-5-yne-4,7-diol.
8. The aqueous dispersion according to claim 1, comprising
N-methyl-2-pyrrolidone.
9. The aqueous dispersion according to claim 1, further comprising
at least one defoamer.
10. The aqueous dispersion according to claim 1, having a pH of 9
to 11, and comprising: 10 to 30% by weight, based on the
dispersion, of hydrophobic silicon dioxide particles, with a
methanol wettability of 40 to 50, and a BET surface area of 90 to
150 m.sup.2/g; 9 to 16% by weight, based on the proportion of
hydrophobized silicon dioxide particles, of a mono-, di-, and/or
trisubstituted phosphate ester of an ethoxylated primary alcohol
having one, two or three linear C.sub.12-C.sub.14 carbon chains; 5
to 20% by weight, based on the proportion of hydrophobized silicon
dioxide particles, of N,N-dimethylethanolamine; 10 to 20% by
weight, based on the proportion of hydrophobized silicon dioxide
particles, of 1 methyl-2-pyrrolidone; 3 to 7% by weight of
tripropylene glycol and 0.5 to 1.5% by weight of
2,4,7,9-tetramethyldec-5-yne-4,7-diol, based in each case on the
proportion of hydrophobized silicon dioxide particles; 1 to 3% by
weight, based on the proportion of hydrophobized silicon dioxide
particles, of one or more defoamers; and 40 to 70% by weight of
water, based on the dispersion.
11. A formulation which comprises hydrophobized silicon dioxide
particles, at least one binder, at least one dispersing additive,
at least one polyol having 2 to 15 carbon atoms, and a basic
composition, wherein: the hydrophobized silicon dioxide particles
have a methanol wettability of 30 to 60 and are present in the
formulation with a proportion of 0.05 to 5% by weight based on the
formulation; the dispersing additive is at least one phosphate
ester of an ethoxylated alcohol having 8 to 18 carbon atoms, a
proportion of which is 3 to 25% by weight based on the proportion
of the hydrophobized silicon dioxide particles; the basic
composition comprises at least one amine of formulas RNH.sub.2,
R.sub.2NH, and/or R.sub.3N, where R is an alkyl group or a
hydroxyl-substituted alkyl group having in each case 2 to 10 carbon
atoms, and is present with a proportion of 5 to 30% by weight based
on the proportion of hydrophobized silicon dioxide particles; the
at least one polyols is present with a proportion of 1 to 10% by
weight based on the proportion of hydrophobized silicon dioxide
particles; and the pH of the formulation is less than 9.
12. The formulation according to claim 11, further comprising color
pigments and/or inactive fillers.
13. A process for preparing a formulation, comprising adding the
aqueous dispersion according to claim 1 to a binder, color pigment,
and/or inactive filler.
14. A process of manufacturing a coating composition, comprising
adding the aqueous dispersion according to claim 1 to a coating
base composition.
15. An aqueous dispersion which comprises hydrophobized silicon
dioxide particles, at least one polyol having 2 to 15 carbon atoms,
at least one dispersing additive, a basic composition, and no color
pigments, no inactive fillers, and no binders, wherein: the
hydrophobized silicon dioxide particles have a methanol wettability
of 30 to 60 and are present in the dispersion with a proportion of
0.1 to 50% by weight based on the dispersion; a proportion of water
is 30 to 90% by weight based on the dispersion; the dispersing
additive is at least one phosphate ester of an ethoxylated alcohol
having 8 to 18 carbon atoms, a proportion of which is 3 to 25% by
weight based on the proportion of the hydrophobized silicon dioxide
particles; the basic composition consists of at least one amine of
formulas RNH.sub.2, R.sub.2NH, and/or R.sub.3N wherein R is an
alkyl group or a hydroxyl-substituted alkyl group having in each
case 2 to 10 carbon atoms, and is present with a proportion of 5 to
30% by weight based on the proportion of hydrophobized silicon
dioxide particles; the at least one polyol is present with a
proportion of 1 to 10% by weight based on the proportion of
hydrophobized silicon dioxide particles; the phosphate ester, the
basic composition, and the at least one polyol are soluble in an
aqueous phase of the dispersion; and the pH of the dispersion is 9
to 11.
Description
The invention relates to an aqueous dispersion which comprises
hydrophobized silicon dioxide particles, and to the preparation and
use thereof. The invention further relates to a formulation which
comprises hydrophobized silicon dioxide particles, and to the
preparation and use thereof.
Important factors in the preparation of dispersions are: good
wetting of the fillers and pigments during processing. This allows
the dispersion times and the introduction of dispersion energy to
be reduced; often, a very low viscosity of the dispersions is
desired; after drying, a high shine should be achieved; the
settling tendency of the solid phase of the dispersion should be at
a minimum, including in the course of prolonged storage, transport
over large distances and under extreme climatic stress; no
flocculation should occur in the dispersion; this is of particular
significance in the production of reproducible hues in the case of
use of nowadays customary colour mixing machines; the dispersion
should be compatible with a multitude of additives.
In order to take account of these factors, dispersants are
generally added to the dispersion. For this purpose, a multitude of
water-soluble dispersants has already been proposed, for example
dispersants based on inexpensive ionic structures such as
polyphosphates (Ullmann's Encyclopedia of Industrial Chemistry,
Sixth Edition, Point 3.2.6., 2002; Th. Staffel, Farbe & Lack
100, 1994) and polyacrylic acids (WO-A-02/14415, WO-A-01/60925, J.
Schroder, Farbe & Lack 91, 1985, 11; R. Hildred, Farbe &
Lack, 1990, 857-859) or amphiphilic structures, i.e. with defined
hydrophobic and hydrophilic blocks, based on nonionic fatty alcohol
ethoxylates or alkylphenol ethoxylates, or anionically modified
derivatives thereof.
Nevertheless, only a few highly filled, low-viscosity, stable
aqueous dispersions which comprise hydrophobized silicon dioxide
particles are known to date. Highly filled dispersions are desired
because this allows the transport costs to be lowered and because,
when they are incorporated into highly filled coating dispersions,
they are not to be diluted again with products having a high water
content.
DE-A-10316661 discloses a highly filled, low-viscosity dispersion
which contains 5 to 50% by weight of hydrophobized silicon dioxide
particles, and a dispersant of the general formula
R.sup.1-COO--(CH.sub.2--CH(Ph)-O).sub.a--(C.sub.nH.sub.2n-xR.sup.2.sub.x--
-O).sub.b--R.sup.3. However, this dispersion leads only to
moderately long-lasting coatings in the application.
It is therefore an object of the invention to provide a
low-viscosity dispersion with a high proportion of hydrophobized
silicon dioxide particles, which has a high stability and, after
processing to aqueous formulations, again builds up a significant
structural viscosity.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the viscosity (in mPas) of an exemplary
dispersion as a function of the pH;
FIGS. 2A and 2B are graphs showing flow curves of coating materials
based on resins C (.quadrature.=coating material C0,
.cndot.=coating material C2, .diamond.=coating material C4,
.box-solid.=coating material C6); and
FIGS. 3A and 3B are graphs showing yield curves of coating
materials based on resins D (.quadrature.=coating material D0,
.cndot.=coating material D1, .diamond.=coating material D2,
.box-solid.=coating material D3).
The invention provides an aqueous dispersion which comprises
hydrophobized silicon dioxide particles and in each case one or
more dispersing additives, a basic composition, and which is free
of colour pigments, inactive fillers and binders, characterized in
that the hydrophobized silicon dioxide particles have a methanol
wettability of 30 to 60, preferably 35 to 55, and are present in
the dispersion with a proportion of 0.1 to 50% by weight,
preferably 10 to 30% by weight, the proportion of water is 30 to
90% by weight, preferably 50 to 70% by weight, based in each case
on the dispersion, the dispersing additive is at least one
phosphate ester of an ethoxylated alcohol having 8 to 18 carbon
atoms, the proportion of which is 3 to 25% by weight, preferably 6
to 20% by weight and more preferably 9 to 16% by weight, based in
each case on the proportion of the hydrophobized silicon dioxide
particles, the basic composition comprises or consists of one or
more amines of the general formula RNH.sub.2, R.sub.2NH and
R.sub.3N, where R is an alkyl group or a hydroxyl-substituted alkyl
group having 2 to 10 carbon atoms, which may be substituted or
unsubstituted, linear or branched, acyclic or cyclic, and is
present with a proportion of 5 to 30% by weight, preferably 10 to
20% by weight and most preferably 12.5 to 17.5% by weight, based in
each case on the proportion of hydrophobized silicon dioxide
particles, the dispersion further comprises one or more polyols
having 2 to 15 carbon atoms, the proportion of which is 1 to 10% by
weight, preferably 3 to 7% by weight, based in each case on the
proportion of hydrophobized silicon dioxide particles, the
phosphate ester, the basic composition and the polyol being soluble
in the aqueous phase of the dispersion and the pH of the dispersion
being 9 to 11.
An aqueous dispersion shall be understood to mean a dispersion
which contains more than 50% by weight of water, generally more
than 70% by weight of water, based on the liquid phase of the
dispersion.
It has been found that conditions regarding the degree of
hydrophobicity of the hydrophobized silicon dioxide particles used
in the inventive dispersion have to be observed. When the
hydrophobicity of the silicon dioxide particles is too high or too
low, this has adverse effects on the stability of the inventive
dispersion. A suitable measure of the hydrophobicity is the
methanol wettability.
In the determination of the methanol wettability, in each case 0.2
g (.+-.0.005 g) of hydrophobic silicon dioxide particles is weighed
into transparent centrifuge tubes. 8.0 ml of a methanol/water
mixture containing one of 10, 20, 30, 40, 50, 60, 70 and 80% by
volume of methanol are added to each weighed sample. The closed
tubes are shaken for 30 seconds and then centrifuged at 2500
min.sup.-1 for 5 minutes. The sediment volumes are read off,
converted to percent and plotted graphically against the methanol
content (% by volume). The turning point of the curve corresponds
to the methanol wettability. The higher the methanol wettability,
the greater the hydrophobicity of the silicon dioxide
particles.
In the inventive dispersion, the methanol wettability is 30 to 60.
Suitable commercially obtainable hydrophobized silicon dioxide
particles which meet this condition are, for example, AEROSIL.RTM.
R972, AEROSIL.RTM. R974, AEROSIL.RTM. R104, AEROSIL.RTM. R106 and
AEROSIL.RTM. R9200, all from Evonik Degussa.
The hydrophobized silicon dioxide particles can preferably be
obtained by hydrophobizing fumed silicon dioxide particles. Fumed
particles are understood to mean those produced by flame hydrolysis
or flame oxidation. Fumed silicon dioxide particles are described,
for example, in Ullmann's Encyclopedia of Industrial Chemistry,
Vol. A23, page 635, 5.sup.th Edition. These particles are generally
present in the form of aggregated primary particles and have, on
their surface, reactive sites which can react with a hydrophobizing
agent. The hydrophobized silicon dioxide particles used for the
inventive dispersion preferably have a BET surface area of 50 to
300 m.sup.2/g, more preferably of 70 to 200 m.sup.2/g and most
preferably of 90 to 150 m.sup.2/g.
In addition, it has been found to be advantageous when the
hydrophobized silicon dioxide particles in the inventive dispersion
have a mean particle size (median) of 200 nm or less. Particular
preference is given to a range of 100 to 200 nm.
A further essential constituent of the inventive dispersion is at
least one phosphate ester of an ethoxylated alcohol which contains
8 to 18 carbon atoms. The dispersion preferably comprises a mono-,
di- and/or trisubstituted phosphate ester of an ethoxylated primary
alcohol with one, two or three linear C.sub.12-C.sub.14 carbon
chains.
In addition, the inventive dispersion comprises a basic composition
which comprises or consists of one or more amines of the general
formula RNH.sub.2, R.sub.2NH and R.sub.3N. The basic composition
preferably consists of one or more amines of the general formula
RNH.sub.2, R.sub.2NH and R.sub.3N. This amine is preferably a
primary, secondary or tertiary amine or an amino alcohol having in
each case 2 to 10 carbon atoms. Suitable compounds are, for
example, monoethanolamine, diethanolamine, triethanolamine,
monoisopropanolamine, diisopropanolamine, triisopropanolamine,
N,N-dimethylisopropanolamine, 3-amino-1-propanol,
1-amino-2-propanol, 2-amino-2-methyl-1-propanol, 2-pyrrolidone,
N-methyl-2-pyrrolidone, N-ethylpyrrolidone, N-vinyl-pyrrolidone,
1,3-dimethylimidazolidone and piperidine.
Particular preference is given to an inventive dispersion which
comprises N,N-dimethylethanolamine
(Me.sub.2N(CH.sub.2).sub.2OH).
A further essential constituent of the inventive dispersion is a
polyol which contains 2 to 15 carbon atoms. The polyol is
preferably selected from the group comprising ethylene glycol,
propylene glycol, butylene glycol, diethylene glycol, triethylene
glycol, tripropylene glycol, trimethylolpropane, pentaerythritol,
neopentyl glycol, glycerol, diethylene glycol monomethyl ether,
diethylene glycol monoethyl ether, diethylene glycol monobutyl
ether, dipropylene glycol monoethyl ether, acetylene glycols such
as 2,4,7,9-tetramethyldec-5-yne-4,7-diol, or acetylene glycol
derivatives.
The inventive dispersion may preferably comprise tripropylene
glycol, 2,4,7,9-tetramethyldec-5-yne-4,7-diol or a mixture of the
two.
The inventive aqueous dispersion may further comprise
N-methyl-2-pyrrolidone. The proportion of N-methyl-2-pyrrolidone is
preferably 1 to 20% by weight based on the proportion of
hydrophobized silicon dioxide particles.
In addition, an aqueous dispersion which comprises
N,N-dimethylethanolamine and 1-methyl-2-pyrrolidone may be
advantageous.
The inventive dispersion may further comprise one or more
preferably silicone-free defoamers. The proportion thereof is
preferably 0.5 to 5% by weight and more preferably 1 to 3% by
weight, based in each case on the proportion of hydrophobized
silicon dioxide particles.
A particularly advantageous inventive dispersion has been found to
be one which has a pH of 9 to 11 and contains 10 to 30% by weight,
based on the dispersion, of hydrophobic silicon dioxide particles
with a methanol wettability of 40 to 50, with a BET surface area of
90 to 150 m.sup.2/g, 9 to 16% by weight, based on the proportion of
hydrophobized silicon dioxide particles, of a mono-, di- and/or
trisubstituted phosphate ester of an ethoxylated primary alcohol
having one, two or three linear C.sub.12-C.sub.14 carbon chains, 5
to 20% by weight, based on the proportion of hydrophobized silicon
dioxide particles, of N,N-dimethylethanolamine, 10 to 20% by
weight, based on the proportion of hydrophobized silicon dioxide
particles, of 1-methyl-2-pyrrolidone, 3 to 7% by weight of
tripropylene glycol and 0.5 to 1.5% by weight of
2,4,7,9-tetramethyldec-5-yne-4,7-diol, based in each case on the
proportion of hydrophobized silicon dioxide particles, 1 to 3% by
weight, based on the proportion of hydrophobized silicon dioxide
particles, of one or more defoamers and 40 to 70% by weight of
water, based on the dispersion.
A suitable dispersion apparatus for preparing the inventive aqueous
dispersion is any apparatus which is capable of enabling intensive
wetting of the hydrophobic powder with the aqueous phase. In the
coatings industry, it is common practice to use dissolvers for this
purpose, the relatively simple construction of which enables a mode
of production which is low in maintenance and easy to clean.
According to the required viscosity or else filling level of the
aqueous dispersion of hydrophobic fumed silica to be obtained,
however, intensive dispersion or post-grinding is necessary. The
post-grinding can be effected, for example, in stirred ball mills.
However, intensive shearing with the aid of rotor/stator machines
is sufficient in many cases. An appropriate combination of wetting
and dispersing means is that of the rotor/stator machines from
Ystral, which enable the powder to be sucked in and, after the
closure of the powder intake orifice, to be dispersed with
intensive shearing.
Especially in the case of rotor/stator machines, in which air can
be sucked in and hence foam can be formed, it has been found to be
advantageous to initially charge only a portion of the water
required and to incorporate a portion of the hydrophobic silicon
dioxide. From a particular amount of hydrophobic silicon dioxide,
approx. 25% by weight based on the total amount of hydrophobic
silicon dioxide to be incorporated, the defoaming action thereof is
detectable. Only then are the proportions of water and hydrophobic
silicon dioxide yet to be added and the further constituents of the
dispersion added.
The invention further provides a formulation which comprises
hydrophobized silicon dioxide particles, one or more binders, one
or more dispersing additives and a basic composition, in which the
hydrophobized silicon dioxide particles have a methanol wettability
of 30 to 60, preferably 35 to 55, and are present in the
formulation with a proportion of 0.05 to 5% by weight, the
dispersing additive is at least one phosphate ester of an
ethoxylated alcohol having 8 to 18 carbon atoms, the proportion of
which is 3 to 25% by weight, preferably 6 to 20% by weight and more
preferably 9 to 16% by weight, based in each case on the proportion
of the hydrophobized silicon dioxide particles, the basic
composition comprises or consists of one or more amines of the
general formula RNH.sub.2, R.sub.2NH and R.sub.3N, where R is an
alkyl group or a hydroxyl-substituted alkyl group having 2 to 10
carbon atoms, which may be substituted or unsubstituted, linear or
branched, acyclic or cyclic, and is present with a proportion of 5
to 30% by weight, preferably 10 to 20% by weight and most
preferably 12.5 to 17.5% by weight, based in each case on the
proportion of hydrophobized silicon dioxide particles, the
dispersion further comprises one or more polyols having 2 to 15
carbon atoms, the proportion of which is 1 to 10% by weight,
preferably 3 to 7% by weight, based in each case on the proportion
of hydrophobized silicon dioxide particles, and the pH of the
formulation being less than 9, preferably 8 to 8.9.
Suitable binders may be the resins customary in paints and coatings
technology, as described, for example, in "Lackharze, Chemie,
Eigenschaften and Anwendungen [Coating resins, chemistry,
properties and applications], Eds. D. Stoye, W. Freitag, Hanser
Verlag, Munich, Vienna, 1996".
Examples include the polymers and copolymers of (meth)acrylic acid
and esters thereof, optionally bearing further functional groups,
with further olefinically unsaturated compounds, for example
styrene, polyetherpolyols, polyesterpolyols, polycarbonatepolyols,
polyurethanepolyols and epoxy resins, and also any mixtures of
these polymers, and also fatty acid-modified "alkyd resins"
prepared by polycondensation, as described in Ullmann, 3.sup.rd
Edition, Volume 11, page 334 ff.
In addition, the polymer components used may be organic compounds
bearing hydroxyl groups, for example polyacrylate-, polyester-,
polycaprolactone-, polyether-, polycarbonate- and
polyurethanepolyols, and hydroxy-functional epoxy resins, and also
any mixtures of these polymers. Especially aqueous or
solvent-containing or solvent-free polyacrylate- and
polyesterpolyols and any mixtures thereof are used.
Polyacrylatepolyols are copolymers of monomers, some of which have
hydroxyl groups, with other olefinically unsaturated monomers, for
example esters of (meth)acrylic acid, styrene, alpha-methylstyrene,
vinyltoluene, vinyl esters, mono- and dialkyl maleates and
fumarates, alpha-olefins and further unsaturated oligomers and
polymers.
The inventive formulation may further comprise colour pigments
and/or inactive fillers.
The colour pigments may be of organic or inorganic nature. Examples
include barium sulphate, lead oxides, lead silicates, iron oxides,
phthalocyanine complexes, titanium dioxides, zinc oxides and zinc
sulphide.
The inventive formulation may further comprise inactive fillers.
Inactive fillers are understood to mean fillers which are known to
those skilled in the art and influence the rheological properties
of the formulation only insignificantly, if at all. Examples
include calcium carbonate, diatomaceous earth, mica, kaolin, chalk,
quartz and talc.
Colour pigments and/or inactive fillers are typically present in
proportions totalling 10 to 70% by weight, preferably 30 to 50% by
weight, based on the total solids content of the formulation.
The total solids content of the formulation, which is composed of
hydrophobized silicon dioxide particles, binders and any colour
pigments and inactive fillers, is preferably 40 to 60% by weight
based on the formulation.
The invention further provides a process for preparing the
formulation, in which the inventive aqueous dispersion is used.
The invention further provides for the use of the inventive aqueous
dispersion or of the inventive formulation as an additive to
waterborne surfacers in the automobile industry, as a coating
constituent in can- and coil-coating processes, as an additive in
water-based UV-curable formulations, for example for wood
protection, and as a constituent of coating protection films.
EXAMPLES
Example 1
According to Invention
6.36 kg of Hydropalat.RTM. 7003 from Cognis, 1.27 kg of
dimethylethanolamine (DMEA), 0.19 kg of BYK.RTM. 011 from Byk
Chemie, 0.19 kg of Surfynol.RTM. 104 from Air Products, 1.91 kg of
1-methyl-2-pyrrolidone and 0.63 kg of tripropylene glycol were
introduced with stirring into 21.19 kg of water.
The mixing was followed by the commencement of the intake of the
hydrophobized silicon dioxide particles by suction with the aid of
a Conti TDS 3 rotor-stator machine. After approx. 30 minutes, 12.80
kg of Aerosil.RTM. R972 from Evonik Degussa had been sucked in.
Shearing was now continued for another 30 minutes, followed by
dilution with 16.15 kg of demineralized water.
A dispersion with a content of hydrophobized silicon dioxide
particles of 21% by weight was obtained. The pH of the dispersion
is 10. This was adjusted to values down to 4 with addition of
hydrochloric acid (1 M).
This dispersion is D1.
Example 2
According to Invention
A jacketed dispersing vessel is initially charged with 312.5 g of
demineralized water, 100.0 g of Hydropalat.RTM. 7003, 6.0 g of
DMEA, 3.0 g of BYK.RTM. 011, 3.0 g of Surfynol.RTM. 104 E, 30.0 g
of 1-methyl-2-pyrrolidone and 10.0 g of tripropylene glycol, which
were mixed with the aid of a Dispermat.RTM. laboratory dissolver
from VMA-Getzmann GmbH (toothed disc of diameter 70 mm) at 200
revolutions per minute. Aerosil.RTM. R972 was then added in
portions and dispersed at 2400 revolutions per minute. After
approx. 80 g of Aerosil.RTM. R972, further Aerosil.RTM. R972 is
added in alternation with further water (total of 339.5 g of
water). At 170 g of Aerosil.RTM. R972, the entire amount of water
had been added. Then a further 30 g of Aerosil.RTM. R972 and 6 g of
DMEA are incorporated in alternation into the dispersion. In total,
200 g of Aerosil.RTM. R972 were incorporated (20 percent
dispersion).
Subsequently, dispersion is continued with the dissolver at 2400
revolutions per minute for a further 15 min. In order to achieve
good dispersion of the Aerosil, there is finally dispersion at 7000
revolutions per minute with the aid of an Ultra Turrax
(rotor/stator dispersion unit of the Ultra-Turrax T50 type from
Ika-Werke with the S50N-G45G dispersion tool) for 30 min. In the
course of this, the jacketed dispersing vessel is cooled with
water, such that the temperature is approx. 30.degree. C.
The pH of the dispersion is 10.2, the viscosity 82 mPas at 10
s.sup.-1 and 72 mPas at 100 s.sup.-1 (all viscosity values reported
in the examples are based on a temperature of 23.degree. C.).
Example 3
According to Invention
A jacketed dispersing vessel is initially charged with 312.5 g of
demineralized water, 100.0 g of Hydropalat.RTM. 7003, 6.0 g of
DMEA, 3.0 g of BYK.RTM. 011, 3.0 g of Surfynol.RTM. 104 E, 30.0 g
of 1-methyl-2-pyrrolidone and 10.0 g of tripropylene glycol, which
are mixed with the aid of a Dispermat.RTM. laboratory dissolver
from VMA-Getzmann GmbH (toothed disc of diameter 70 mm) at 200
revolutions per minute. Aerosil.RTM. R974 was then added in
portions and dispersed at 2400 revolutions per minute. After
approx. 70 g of Aerosil.RTM. R974, further Aerosil.RTM. R974 is
added in alternation with further water (total of 339.5 g of
water). At 170 g of Aerosil.RTM. R974, the entire amount of water
had been added. Then a further 30 g of Aerosil.RTM. R974 and 6 g of
DMEA are incorporated in alternation into the dispersion.
Subsequently, dispersion is continued with the dissolver at 2400
revolutions per minute for a further 15 min. In order to achieve
good dispersion of the Aerosil, there is finally dispersion at 7000
revolutions per minute with the aid of an Ultra Turrax
(rotor/stator dispersion unit of the Ultra-Turrax T50 type from
Ika-Werke with the S50N-G45G dispersion tool) for 30 min. In the
course of this, the jacketed dispersing vessel is cooled with
water, such that the temperature is approx. 30.degree. C.
The pH of the dispersion is 10.1, the viscosity 1036 mPas at 10
s.sup.-1 and 390 mPas at 100 s.sup.-1.
Example 4
Comparative
A jacketed dispersing vessel is initially charged with 312.5 g of
demineralized water, 100.0 g of Hydropalat.RTM. 7003, 6.0 g of
DMEA, 3.0 g of BYK.RTM. 011, 3.0 g of Surfynol.RTM. 104 E, 30.0 g
of 1-methyl-2-pyrrolidone and 10.0 g of tripropylene glycol, which
are mixed with the aid of a Dispermat.RTM. laboratory dissolver
from VMA-Getzmann GmbH (toothed disc of diameter 70 mm) at 200
revolutions per minute. Aerosil.RTM. R202 was then added in
portions and dispersed at 2400 revolutions per minute. The powder
is wetted very poorly and is dispersed in only poorly. After only
44 g (9% by weight), the dispersion became very viscous and no
further Aerosil.RTM. R202 could be incorporated.
Example 5
Comparative
A jacketed dispersing vessel is initially charged with 312.5 g of
demineralized water, 6.0 g of DMEA, 3.0 g of BYK.RTM. 011, 3.0 g of
Surfynol.RTM. 104 E, 30.0 g of 1-methyl-2-pyrrolidone and 10.0 g of
tripropylene glycol, which are mixed with the aid of a
Dispermat.RTM. laboratory dissolver from VMA-Getzmann GmbH (toothed
disc of diameter 70 mm) at 200 revolutions per minute. Aerosil.RTM.
R972 was then added in portions and dispersed at 2400 revolutions
per minute. The powder is wetted very poorly and is dispersed in
only poorly. After only 40 g (10% by weight), the dispersion became
very viscous.
Even the addition of further water (104 g) did not bring any
significant improvement; only a further 6 g of Aerosil.RTM. R972
could be dispersed in. Further addition of 2.8 g of DMEA did not
bring any improvement either.
Example 6
Comparative
A jacketed dispersing vessel is initially charged with 312.5 g of
demineralized water, 100.0 g of Hydropalat.RTM. 7003, 6.0 g of
DMEA, 3.0 g of BYK.RTM. 011, 3.0 g of Surfynol.RTM. 104 E and 30.0
g of 1-methyl-2-pyrrolidone, which are mixed with the aid of a
Dispermat.RTM. laboratory dissolver from VMA-Getzmann GmbH (toothed
disc of diameter 70 mm) at 200 revolutions per minute. Aerosil.RTM.
R972 was then added in portions and dispersed at 2400 revolutions
per minute. After approx. 80 g of Aerosil.RTM. R972, further
Aerosil.RTM. R972 is added in alternation with further water (total
of 339.5 g of water). At 160 g of Aerosil.RTM. R972, the entire
amount of water had been added. Then a further 40 g of Aerosil.RTM.
R972 and 6 g of DMEA are incorporated in alternation into the
dispersion. In total, 200 g of Aerosil.RTM. R972 were incorporated
(20% dispersion).
Subsequently, dispersion is continued with the dissolver at 2400
revolutions per minute for a further 15 min. In order to achieve
good dispersion of the Aerosil, there is finally dispersion at 7000
revolutions per minute with the aid of an Ultra Turrax
(rotor/stator dispersion unit of the Ultra-Turrax T50 type from
Ika-Werke with the S50N-G45G dispersion tool) for 30 min. In the
course of this, the jacketed dispersing vessel is cooled with
water, such that the temperature is approx. 30.degree. C. The pH of
the dispersion is 10.1, the viscosity 69 mPas at 10 s.sup.-1 and 57
mPas at 100 s.sup.-1.
Even by treatment with ultrasound, the dispersion is difficult to
deaerate and is therefore only of limited suitability for
applications in the paints and coatings sector.
Example 7
Comparative
100 g of Aerosil.RTM. R972 are incorporated by means of a dissolver
at a setting of approx. 2500 rpm in portions into 192.5 g of
demineralized water, 88 g of a mixture of the dispersant
C.sub.18H.sub.37-COO--(C.sub.2H.sub.4O).sub.100H and of the amine
oxide-containing maleic anhydride copolymer from Example 1,
EP-A-1026178, in a mixing ratio of 85:15, as a 40 percent solution
in water, and 7.5 g of Tego Foamex.RTM. 810, Degussa AG. A total of
1.79 g of 90% 2-amino-2-methyl-1-propanol solution are used to keep
the pH at 10. After the remaining 110.21 g of demineralized water
have been added, the mixture is homogenized further at 3000 rpm for
15 minutes. The actual dispersion is subsequently effected with the
aid of an Ultra Turrax at 7000 rpm for 30 minutes.
d.sub.50(V) is 193 nm; the viscosity is 310 mPas at 10 s.sup.-1,
and 275 mPas at 100 s.sup.-1.
Table 1 shows the composition and properties of the dispersions of
Examples 1 to 7.
Inventive Examples 1 to 3 lead to dispersions with low viscosity,
which increases only insignificantly even in the course of
prolonged storage. Table 2 reproduces the values of the viscosity
(in mPas) of the dispersion prepared in Example 1 as a function of
the shear rate (in s.sup.-1), immediately after the preparation of
the dispersion, after 1 month of storage and after 6 months of
storage.
The mean particle diameter d.sub.50 (median) of the hydrophobized
silicon dioxide particles behaves analogously. It is 156 nm
immediately after preparation, 174 nm after 1 month of storage and
194 nm after 6 months of storage.
FIG. 1 shows the viscosity (in mPas) as a function of the pH. In
the range from 9 to 11, the dispersion exhibits a particularly low
viscosity. At pH values less than 9, the viscosity rises again.
This structural viscosity leads to an increase in the stability of
a dispersion which, for example, also comprises fillers and/or
colour pigments, since it greatly reduces the settling thereof.
TABLE-US-00001 TABLE 1 Composition and properties of the
dispersions According to invention Comparative 1 2 3 4 5 6 7
AEROSIL .RTM. m.sup.2/g R 972 R 972 R974 R202 R972 R972 R972 BET
surface area g 110 110 170 100 110 110 110 Methanol wettability 45
45 45 75 45 45 45 12800 200.0 200.0 44.0 40.0 200.0 100.0
Demineralized water g 37340 652.0 652.0 312.5 312.5 652.0 355.7
Hydropalat .RTM. 7003 g 6360 100.0 100.0 100.0 -- 100.0 -- DMEA g
1270 12.0 6.0 6.0 6.0 12.0 1.61 tripropylene glycol g 630 10.0 10.0
10.0 10.0 -- -- Surfynol .RTM. 104 E g 190 3.0 3.0 3.0 3.0 3.0 --
BYK .RTM. 011 g 190 3.0 3.0 3.0 3.0 3.0 -- Nmethyl2pyrrolidone g
1910 30.0 30.0 30.0 30.0 30.0 -- 85:15 g -- -- -- -- -- -- 35.20
C.sub.18H.sub.37COO--(C.sub.2H.sub.4O) .sub.100 H/MA copolymer*
Tego Foamex .RTM. 810 g -- -- -- -- -- -- 7.5 pH 10 10.2 -- n.d.**
n.d. 10.1 10 Viscosity 10 s.sup.-1 mPas 70 82 1036 n.d. n.d. 69 310
Viscosity 100 s.sup.-1 mPas 60 72 390 n.d. n.d. 57 272 Mean
particle diameter*** Median .mu.m 0.096 0.224 n.d. -- -- 0.562 --
Mean .mu.m 0.105 0.261 n.d. -- -- 38.12 -- *from Example 1,
EPA1026178, containing amine oxide; **n.d. = not determined;
***determined with Horiba LA 910
TABLE-US-00002 TABLE 2 Viscosity of the dispersion from Example 1
as a function of shear rate and storage After preparation 1 month
of storage 6 months of storage Shear rate Viscosity Schear rate
Viscosity Schear rate Viscosity [1/s] [mPa s] [1/s] [mPa s] [1/s]
[mPa s] 0.1 80.06 0.1 128.4 0.1 166.2 0.1374 79.93 0.1374 131.7
0.1374 164.7 0.2593 85.82 0.2593 129.8 0.2593 162 0.3562 83.48
0.3562 127.7 0.3562 161.2 0.4894 81.39 0.4894 128.3 0.4894 158.7
0.6723 79.27 0.6723 125.7 0.6723 156.3 0.9237 76.97 0.9237 124.7
0.9237 154.2 1.269 75.26 1.269 122.6 1.269 151.5 1.743 74.33 1.743
120 1.743 148.2 2.395 72.86 2.395 117.5 2.395 144.6 3.29 71.39 3.29
114.7 3.29 140.6 11.72 69.91 11.72 111.6 11.72 136.2 16.1 68.25
16.1 108.2 16.1 131.8 22.12 66.54 22.12 104.8 22.12 127.5 30.39
64.72 30.39 101.4 30.39 123.4 41.75 62.83 41.75 98.29 41.75 120.2
57.36 60.96 57.36 95.47 57.36 117.7 108.3 59.24 108.3 93.23 108.3
116.4 148.7 57.63 148.7 91.71 148.7 116.4 204.3 56.27 204.3 90.96
204.3 117.5 280.7 55.2 280.7 90.84 280.7 119.1 385.7 54.42 385.7
90.98 385.7 120.2 529.9 53.88 529.8 90.9 529.9 119.9 727.9 53.35
727.9 90.04 727.9 117.7 1000 52.79 1000 88.24 1000 113.8
Comparative Example 4 shows the influence of the methanol
wettability of the hydrophobized silicon dioxide particles used. In
Comparative Example 4, Aerosil.RTM. R202 with a methanol
wettability of 75 is used, compared to Aerosil.RTM. R972 in
Inventive Examples 1 and 2. Aerosil.RTM. R972 and Aerosil.RTM. R974
have comparable BET surface areas. Nevertheless, only small
proportions can be incorporated.
In contrast to this, Inventive Example 3 shows that Aerosil.RTM.
R974 with a higher BET surface area than Aerosil.RTM. R972 but with
a comparable methanol wettability can also be incorporated in high
proportions.
Comparative Example 5 shows the influence of the phosphate ester on
the properties of the inventive dispersion. In this case, the
hydrophobized silicon dioxide particles are wetted very poorly and
the result is high-viscosity dispersions with a low filler
content.
Comparative Example 6 shows the influence of the polyol on the
properties of the inventive dispersion. Without a sufficient amount
of polyol, sufficient foaming of the dispersion is not ensured. In
the particle size determination, fractions with a high diameter are
determined.
Comparative Example 7 is taken from DE-A-10316661 (Example 1
there). Table 1 shows that the viscosity of this dispersion is
about four times higher than the viscosity of the inventive
dispersion from Examples 1 and 2.
The application of a formulation comprising binders and colour
pigments and if appropriate also inactive fillers is simplified
considerably, since there is no runoff of the dispersion after
application. Since a low viscosity is attained under shear, i.e. in
the course of processing, the formulation can be processed very
efficiently by spraying or else dipping. Especially in the case of
dipping, a low viscosity is needed also to flow into ultrasmall
cavities and gaps.
Examples of formulations comprising binders, colour pigments and
inactive fillers are listed below.
TABLE-US-00003 TABLE 3 Grinding formulations A [all in g] AI AII
AIII AEROSIL .RTM. R972 -- 0.33 1.00 Bayhydrol .RTM. D270 3.76 3.76
3.76 Water 8.28 8.28 8.28 DMEA 10% in water 0.53 0.53 0.53 Surfynol
.RTM. 104E 0.48 0.48 0.48 BYK .RTM. 011 0.89 0.89 0.89 Tronox .RTM.
R-FD-I 9.64 9.64 9.64 Bayferrox .RTM. 303T 0.11 0.11 0.11 Blanc
fixe micro 9.7 9.7 9.7 talc, IT extra 2.37 2.37 2.37 Sum 35.76
36.09 36.76 Bayhydrol .RTM. D 270, water-dilutable polyester resin
from Bayer AG; Tronox .RTM. R-FD-I, titanium dioxide from Kerr
McGee Pigments GmbH & Co.KG), Bayferrox .RTM. 303 T, iron oxide
black, Bayer AG; Blanc fixe Micro, barium sulphate, Sachtleben
GmbH; Micro Talc IT Extra, talc, Norwegian Talc; BYK .RTM. 011,
silicone-free defoamer, from Byk Chemie; Surfynol .RTM. 104E,
2,4,7,9-tetramethyldec-5-yne-4,7-diol, from Air Products
TABLE-US-00004 TABLE 4 Additive composition B (all in g) Hydropalat
7003 60.25 N-methylpyrrolidone 18.07 DMEA 12.05 tripropylene glycol
6.01 BYK 011 1.81 Surfynol E104 1.81 Sum 100
TABLE-US-00005 TABLE 5 Resins C and D (all in g) C D Bayhydrol D270
6.76 7.86 Bayhytherm 3146* 32.51 37.80 Bayhytherm VP LS 2153 37.36
43.45 Cymel 327* 7.65 8.90 BYK 346* 0.88 1.02 DMEA 10% in water
2.95 0.98 water 11.90 -- Sum 100 100 *Bayhytherm 3146 aliphatic,
self-crosslinking urethane resin, Bayer AG; Cymel .RTM. 327,
melamine resin, Dyno Cytec; Byk .RTM. 346, polyether-modified
dimethylpolysiloxane solution
TABLE-US-00006 TABLE 6 Formulation based on resin C Comparative
According to invention C0 Cl C2 C3 C4 C5 C6 D1 g -- -- -- 1.62 4.90
AI g 35.76 -- -- 35.76 35.76 AII g -- 36.09 -- -- -- AIII g -- --
36.76 -- -- Borchi Gel PW 25 * g 0.33 1.00 B g 0.78 0.78 0.78 0.78
0.78 0.64 -- Resin g 57.48 57.48 57.48 57.48 57.48 57.48 57.48
Water g 5.97 5.64 4.97 5.64 4.97 4.49 1.86 Sum g 100.00 100.00
100.00 100.00 100.00 100.00 100.00 Solids % by wt. 49 49 49 49 49
49 49 Hydrophobic SiO.sub.2 % by wt. 0 0.33 1 0.33 1 0.33 1 Borchi
.RTM. Gel PW 25, from Borchers; structurally viscous thickener for
adjusting the viscosity in the low and moderate shear segment;
TABLE-US-00007 TABLE 7 Formulation based on resin D According to
Comparative invention D0 D1 D2 D3 D4 D1 g -- 4.9 9.8 AI g 35.76
35.76 35.76 All g AIII g 36.76 Borchi Gel g 1 PW 25 B g 0.81 0.81
0.81 Resin g 59.34 59.34 59.34 59.34 59.34 Water g 4.09 3.09 3.09
Sum g 100.00 100.00 100.00 100.00 104.9 Solids % by wt. 54 55 55 55
53 Hydrophobic % by wt. 0 1 1 1 2 SiO.sub.2
Preparation and Testing of the Formulations (Coating Materials)
Predispersion: Mix millbase with dissolver for 5 min
Dispersion: Disperse millbase with Dispermat SL 603, 100 ml of 1 mm
glass beads, at 3000 rpm, until grindometer <10 .mu.m.
Letdown: The millbase is initially charged and the letdown mixture,
additive mixture and water are added with stirring. Homogenize with
dissolver for 5 min.
Viscosity of the coating materials: Coating materials: Flow curves
and yield tests Flow curve: Preliminary shear=50 s.sup.-1 (30 s)
Rest (600 s) Measurement=0.1 s.sup.-1 to 500 s.sup.-1 (150 s) Yield
test: 120 s at 500 s.sup.-1 300 s at 0.5 s.sup.-1
Application: 18 mm/s with Erichsen automatic applicator and runoff
blade on glass plates. Glass plates were placed vertically for a
period of 3 min, then the runoff was assessed.
Settling behaviour: The samples were stored at 20.degree. C. and
40.degree. C. for four weeks and then the sediment height was
measured with a ruler. The percentage ratio between sediment and
supernatant phase was calculated therefrom and reported as the
result.
Results
TABLE-US-00008 TABLE 8 Formulation based on resin C According to
Comparative invention C0 C1 C2 C3 C4 C5 C6 pH 8.64 8.69 8.61 8.64
8.68 8.68 8.64 Flow time * 17 20 26 120 20 20 22 * DIN 4 cup in
s
TABLE-US-00009 TABLE 9 Formulation based on resin D Comparative
According to invention D0 D1 D2 D3 D4 pH 8.29 8.24 8.27 8.26
8.47
Settling behaviour: Here, the supernatant phase is reported as a
percentage relative to the total fill level of the coating
material; a small value means a better floating behaviour or
antisettling behaviour.
TABLE-US-00010 TABLE 10 Settling behaviour, formulation based on
resin C According to Comparative invention C0 C1 C2 C3 C4 C5 C6 At
20.degree. C. 66 53 34 58 29 56 49 At 40.degree. C. 68 56 39 64 54
62 40
TABLE-US-00011 TABLE 11 Settling behaviour, formulation based on
resin D Comparative According to invention D0 D1 D2 D3 D4 At
20.degree. C. 23 5 5 21 1 At 40.degree. C. 35 5 32 23 1 Values for
TABLES 10 and 11 in %
Runoff behaviour: The run limit at which no runs extend down to the
next thickest strip was assessed.
TABLE-US-00012 TABLE 12 Maximum layer thickness in .mu.m
Comparative According to invention C0 C2 C4 C6 Maximum layer .mu.m
100 125 225 175 thickness
FIGS. 2 and 3 show the flow and yield curves of formulations
(coating materials) based on resins C and D.
For FIG. 2A and FIG. 2B:
.quadrature.=coating material C0, .circle-solid.=coating material
C2, .diamond.=coating material C4, .box-solid.=coating material
C6.
For FIG. 3A and FIG. 3B:
.quadrature.=coating material D0, .circle-solid.=coating material
D1, .diamond.=coating material D2, .box-solid.=coating material
D3,
It is clearly evident from the flow curves shown in FIGS. 2A and 2B
that the formulations based on the dispersion with 1% by weight of
Aerosil.RTM. R 972 cause a marked structural viscosity. At low
shear rates, this enables very good stabilization of pigments and
inactive fillers. The formulation based on 1% by weight of Borchi
Gel also causes a relatively high viscosity, but this decreases
only slightly at higher shear. However, a low viscosity is
preferable in the course of dipping, rolling, spraying, in order to
reach all regions of the surface to be treated.
By virtue of high viscosities at low shear rates, it is also
possible to achieve a thicker layer without the material running
off/dripping off again.
In contrast, the formulation based on 1% by weight of Aerosil.RTM.
R 972 powder does not have this behaviour.
The yield curves shown in FIGS. 3A and 3B are intended to show how
rapidly the viscosity determined by the flow curves is
reestablished in the case of rapid change in the shear rate. In the
case of ideal structural viscosity, the viscosity, as soon as the
shear rate falls, should rise again and have a constant value.
The somewhat retarded buildup in the viscosity is desired, since it
helps to achieve better flow of the coating material/paint.
It can be discerned from the yield curves that there is a rapid
viscosity increase again for the formulation based on a dispersion
with 1% by weight of Aerosil.RTM. R 972.
* * * * *